Discrete-Time Low-Pass Filter with Ultra-Sharp Roll-Off Frequency

This paper presents an infinite-impulse response (IIR) low-pass filter that operates in a discrete-time chargerotating manner and achieves a very sharp roll-off characteristic. The key idea is to apply a feedback from the penultimate stage to the first stage, thereby improving the in-band loss without affecting its stopband rejection. Its performance was verified in post-layout simulations in TSMC 28-nm CMOS technology. The filter achieves stopband rejection of 125 dB, with a 3-dB improvement of in-band loss, all at the power consumption of merely 1.51 mW.